Negative Ion Plasma Research Articles

Linear and nonlinear obliquely propagating ion-acoustic waves in magnetized negative ion plasma with non-thermal electrons

AbstractIon-acoustic solitons in magnetized low-β plasma consisting of warm adiabatic positive and negative ions and non-thermal electrons have been studied. The reductive perturbation method is used to derive the Korteweg–de Vries (KdV) equation for the system, which admits an obliquely propagating soliton solution. It is found that due to the presence of finite ion temperature there exist two modes of propagation, namely fast and slow ion-acoustic modes. In the case of slow-mode if the ratio of temperature to mass of positive ion species is lower (higher) than the negative ion species, then there exist compressive (rarefactive) ion-acoustic solitons. It is also found that in the case of slow mode, on increasing the non-thermal parameter (γ) the amplitude of the compressive (rarefactive) soliton decreases (increases). In fast ion-acoustic mode the nature and characteristics of solitons depend on negative ion concentration. Numerical investigation in case of fast mode reveals that on increasing γ, the amplitude of compressive (rarefactive) soliton increases (decreases). The width of solitons increases with an increase in non-thermal parameters in both the modes for compressive as well as rarefactive solitons. There exists a value of critical negative ion concentration (αc), at which both compressive and rarefactive ion-acoustic solitons appear as described by modified KdV soliton. The value of αc decreases with increase in γ.

Behaviour of sheath voltage in negative ion plasma

The sheath voltage in SF6/Xe plasma was measured with the Langmuir probe and compared with the theoretical value calculated from the sheath equation including negative ions. The negative ion density was estimated from the reduction of the electron saturation current. It was found that the observed sheath voltages agree with the theoretical values qualitatively.

Electrostatic double layers in a warm negative ion plasma with nonextensive electrons

Abstract The electrostatic double layer (DL) structures are studied in negative ion plasma with nonextensive electrons q -distribution. The extended Korteweg–de Vries (EKdV) equation is derived using a reductive perturbation method. It is found that both fast (compressive) and slow (rarefactive) ion acoustic (IA) DLs can propagate in such type of plasmas. The effects of various plasma physical parameters; such as nonextensivity of electrons, presence of negative ions, temperature of both positive and negative ions and different mass ratios of positive to negative ions on the formation of DL structures are discussed in detail with numerical illustrations.

Excitation of lower hybrid waves by a gyrating ion beam in a negative ion plasma

A gyrating ion beam propagating through a magnetized plasma cylinder containing K+ positive ions, electrons, and SF6− negative ions drives electrostatic lower hybrid waves to instability via Cyclotron interaction. Numerical calculations of the unstable mode frequencies and growth rates of both the unstable positive ion and negative ion modes have been carried out for the existing negative ion plasma parameters. It is found that the unstable mode frequencies of both the modes increase, with the relative density of negative ions. In addition, the growth rates of both the unstable modes also increases with relative density of negative ions. Moreover, the growth rates of both the unstable modes scale as the one-third power of the beam density. The frequencies of both the unstable modes also increase with the magnetic fields. The real part of the unstable wave frequency increases as almost the square root of the beam energy.

Nonlinear wave propagation of large amplitude ion-acoustic solitary waves in negative ion plasmas with superthermal electrons

AbstractInvestigation of arbitrary amplitude nonlinear ion-acoustic solitary waves which accompany collisionless positive–negative ion plasmas with high-energy electrons (represented by kappa distribution) is presented. Arbitrary amplitude solitary waves are investigated by deriving an energy-integral equation involving a Sagdeev-like pseudopotential. The existence regions of solitary pulses are, defined precisely, modified by the superthermality of energetic electrons. Furthermore, numerical calculations reveal that both compressive and rarefactive pulses may exist for negative ion mass groups in Titan's atmosphere. The superthermality of energetic electrons are found to modify the existence domains of large amplitude ion-acoustic waves in Titan's atmosphere. The dependence of solitary excitation characteristics on the superthermal parameter, the negative ion concentration, the positive-to-negative ions mass ratio, and the Mach number have been investigated. The present study might be helpful to understand the excitation of fully nonlinear ion-acoustic solitary pulses that may appear in the interplanetary medium and/or in the astrophysical plasmas in general.

Ion-acoustic solitary waves and shocks in a collisional dusty negative-ion plasma

We study the effects of ion-dust collisions and ion kinematic viscosities on the linear ion-acoustic instability as well as the nonlinear propagation of small-amplitude solitary waves and shocks (SWS) in a negative-ion plasma with immobile charged dusts. The existence of two linear ion modes, namely the "fast" and "slow" waves, is shown, and their properties are analyzed in the collisional negative-ion plasma. Using the standard reductive perturbation technique, we derive a modified Korteweg-de Vries-Burger (KdVB) equation which describes the evolution of small-amplitude SWS. The profiles of the latter are numerically examined with parameters relevant for laboratory and space plasmas where charged dusts may be positively or negatively charged. It is found that negative-ion plasmas containing positively charged dusts support the propagation of SWS with negative potential. However, the perturbations with both positive and negative potentials may exist when dusts are negatively charged. The results may be useful for the excitation of SWS in laboratory negative-ion plasmas as well as for observation in space plasmas where charged dusts may be positively or negatively charged.

Characteristics of ion acoustic solitary waves in a negative ion plasma with superthermal electrons

The behavior of ion acoustic solitons in a plasma including positive and negative ions and kappa distributed electrons is studied, using both small amplitude and arbitrary amplitude approaches. The existence regions of compressive and rarefactive solitons will depend on negative to positive ion density ratio (ν) and kappa parameter as well as positive to negative ion mass ratio (Q). The numerical analysis of Sagdeev potential shows that for a chosen plasma with fixed Q, the existence regime of compressive solitons is decreased (increased) by increasing density ratio (kappa parameter), while for rarefactive solitons these conditions are quite opposite. Additionally, the possibility of propagation of both compressive and rarefactive subsonic solitons is investigated. It is found that by increasing negative ions, the existence domains of subsonic solitons are decreased, so that in excess of negative ions subsonic solitons will not propagate even at the presence of superthermal electrons. Indeed, there is a critical negative ion density ratio for all values of kappa, above that only supersonic solitons are observed. Furthermore, in addition to the previous results based on Cairns-distributed electrons [R. A. Cairns et al., Geophys. Res. Lett. 22, 2709 (1995)], which predicted that both compressive and rarefactive solitons can coexist simultaneously, we have also found the regions of ν and κ in which either positive or negative potentials are permitted (i.e., not together). This research will be helpful in understanding the properties of space and laboratory plasmas containing negative ions with energetic electrons.

Ion-acoustic solitons in negative ion plasma with two-electron temperature distributions

Ion–acoustic solitons in a warm positive and negative ion species with different masses, concentrations, and charge states with two electron temperature distributions are studied. Using reductive perturbation method, Korteweg de-Vries (KdV) and modified-KdV (m-KdV) equations are derived for the system. The soliton solution of the KdV and m-KdV equations is discussed in detail. It is found that if the ions have finite temperatures, then there exist two types of modes, namely slow and fast ion-acoustic modes. It is also investigated that the parameter determining the nature of soliton (i.e., whether the system will support compressive or rarefactive solitons) is different for slow and fast modes. For the slow mode, the parameter is the relative temperature of the two ion species; whereas for the fast mode, it is the relative concentration of the two ion species. At a critical concentration of negative ions, both compressive and rarefactive solitons coexist. The amplitude and width of the solitons are discussed in detail at critical concentration for m-KdV solitons. The effect of the relative temperature of the two-electron and cold-electron concentration on the characteristics of the solitons are also discussed.

Simulation of H− ion source extraction systems for the Spallation Neutron Source with Ion Beam Simulator

A three-dimensional ion optical code IBSimu, which is being developed at the University of Jyväskylä, features positive and negative ion plasma extraction models and self-consistent space charge calculation. The code has been utilized for modeling the existing extraction system of the H(-) ion source of the Spallation Neutron Source. Simulation results are in good agreement with experimental data. A high-current extraction system with downstream electron dumping at intermediate energy has been designed. According to the simulations it provides lower emittance compared to the baseline system at H(-) currents exceeding 40 mA. A magnetic low energy beam transport section consisting of two solenoids has been designed to transport the beam from the alternative electrostatic extraction systems to the radio frequency quadrupole.

Two dimensional nonplanar evolution of electrostatic shock waves in pair-ion plasmas

Electrostatic waves in a two dimensional nonplanar geometry are studied in an unmagnetized, dissipative pair-ion plasma in the presence of weak transverse perturbations. The dissipation in the system is taken into account by incorporating the kinematic viscosity of both positive and negative ions in plasmas. The nonplanar Kadomtsev-Petviashvili-Burgers (KPB) as well as the Burgers Kadomtsev-Petviashvili (Burgers KP) equations are derived using the small amplitude expansion method and the range of applicability of both the equations are discussed. The system under consideration is observed to admit compressive rarefactive shocks. The present study may have relevance to understand the formation of two dimensional nonplanar electrostatic shocks in laboratory plasmas.

Ion acoustic solitons in negative ion plasmas with superthermal electrons

Korteweg-de Vries (KdV) equation for electrostatic wave in an unmagnetized negative ion plasma with superthermal electrons is derived using reductive perturbation technique. A generalized Lorentzian distribution (kappa distribution) is assumed for the electrons. The influence of spectral index (kappa) on the soliton is discussed in the presence of the negative ions. It is found that different plasma parameters such as (negative ion temperature, positive ion temperature, negative ion concentration, mass ratio of positive to negative ion) in the presence of superthermal electrons modify the ion acoustic solitary wave structure significantly.

Implosion and explosion of electrostatic cylindrical and spherical shocks in asymmetric pair-ion plasmas

Nonlinear electrostatic shock waves are studied in unmagnetized, dissipative pair-ion plasmas. The dissipation in the system is taken into account by considering the effect of kinematic viscosity of both positive and negative ions in plasmas. The system of fluid equations for asymmetric pair-ion plasma is reduced to Korteweg–deVries–Burgers equation in the limit of small amplitude perturbation. It is observed that the system under consideration admits rarefactive shocks. Keeping in view the practical applications, the nonlinear propagation of both the exploding and imploding shocks is investigated and the differences are expounded in detail. The present study may have relevance in the study of the formation of electrostatic shocks in laser-induced implosion devices, star formation, supernovae explosion, etc.

Modulational instability of ion-acoustic wave packets in quantum pair-ion plasmas

Amplitude modulation of quantum ion-acoustic waves (QIAWs) in a quantum electron-pair-ion plasma is studied. It is shown that the quantum coupling parameter H (being the ratio of the plasmonic energy density to the Fermi energy) is ultimate responsible for the modulational stability of QIAW packets, without which the wave becomes modulational unstable. New regimes for the modulational stability (MS) and instability (MI) are obtained in terms of H and the positive to negative ion density ratio β. The growth rate of MI is obtained, the maximum value of which increases with β and decreases with H. The results could be important for understanding the origin of modulated QIAW packets in the environments of dense astrophysical objects, laboratory negative ion plasmas as well as for the next generation laser solid density plasma experiments.

Effect of Ion Temperature on Soliton Reflection in a Magnetized Positive-Ion–Negative-Ion Plasma With Two Types of Electrons

Analytical investigations are carried out for the soliton propagation and reflection in a magnetized positive-ion-negative-ion plasma having two types of electrons based on the reductive perturbation technique. It is found that this type of plasma does not support rarefactive solitons, which are otherwise found to propagate in negative-ion-containing plasmas with isothermal electrons. This is the consequence of the low-temperature electron component present in the plasma. Two types of compressive solitons, namely, the fast wave soliton and the slow wave soliton, are found to exist, but only the fast compressive solitons will reflect. The effect of ion temperature is to enhance the soliton reflection; the same is the case for an increased number of negative ions. However, the effect of low-temperature electrons is to weaken the soliton reflection. Interestingly, the solitons are found to downshift after their reflection, and this shift is less under the effects of stronger magnetic field, smaller wave propagation angle, and a higher concentration of low-temperature electrons. However, larger amplitude solitons are more downshifted, and the shift is more for higher ion temperature and when the wave propagates with larger phase velocity.

Propagation of three-dimensional ion-acoustic solitary waves in magnetized negative ion plasmas with nonthermal electrons

Properties of small amplitude nonlinear ion-acoustic solitary waves in a warm magneto plasma with positive-negative ions and nonthermal electrons are investigated. For this purpose, the hydrodynamic equations for the positive-negative ions, nonthermal electron density distribution, and the Poisson equation are used to derive the corresponding nonlinear evolution equation; Zkharov–Kuznetsov (ZK) equation, in the small amplitude regime. The ZK equation is analyzed to examine the existence regions of the solitary pulses. It is found that compressive and rarefactive ion-acoustic solitary waves strongly depend on the mass and density ratios of the positive and negative ions as well as the nonthermal electron parameter. Also, it is found that there are two critical values for the density ratio of the negative-to-positive ions (υ), the ratio between unperturbed electron-to-positive ion density (μ), and the nonthermal electron parameter (β), which decide the existence of positive and negative ion-acoustic solitary waves. The present study is applied to examine the small amplitude nonlinear ion-acoustic solitary excitations for the (H+, O2−) and (H+, H−) plasmas, where they are found in the D- and F-regions of the Earth’s ionosphere. This investigation should be helpful in understanding the salient features of the nonlinear ion-acoustic solitary waves in space and in laboratory plasmas where two distinct groups of ions and non-Boltzmann distributed electrons are present.

Cesium control and diagnostics in surface plasma negative ion sources

For efficient and reliable negative ion generation it is very important to improve a cesium control and diagnostics. Laser beam attenuation and resonance fluorescence can be used for measurement of cesium distribution and cesium control. Resonant laser excitation and two-photon excitation can be used for improved cesium ionization and cesium trapping in the discharge chamber. Simple and inexpensive diode lasers can be used for cesium diagnostics and control. Cesium migration along the surface is an important mechanism of cesium escaping. It is important to develop a suppression of cesium migration and cesium accumulation on the extraction system.

Cross-field dust acoustic instability in a dusty negative ion plasma

A cross-field dust acoustic instability in a dusty negative ion plasma in a magnetic field is studied using kinetic theory. The instability is driven by the E×B drifts of the ions. It is assumed that the negative ions are much heavier than the positive ions, and that the dust is negatively charged. The case where the positive ions and electrons are magnetized, the negative ions are marginally unmagnetized, and the dust is unmagnetized is considered. The focus is on a situation where Doppler resonances near harmonics of the positive ion gyrofrequency can affect the spectrum of unstable dust acoustic waves. Application to possible laboratory experimental parameters is discussed.

Electrostatic shocks and solitons in pair-ion plasmas in a two-dimensional geometry

Nonlinear electrostatic waves are studied in unmagnetized, dissipative pair-ion plasmas in the presence of weak transverse perturbations. The dissipation in the system is taken into account by incorporating the kinematic viscosity of both positive and negative ions in plasmas. The Kadomtsev–Petviashvili–Burger equation is derived using the small amplitude expansion method. The Kadomtsev–Petviashvili equation for pair-ion plasmas is also presented by ignoring the dissipative effects. Both compressive and rarefactive shocks and solitary waves are found to exist in pair-ion plasmas. The dependence of compression and rarefaction on the temperature ratios between the ion species is numerically shown. The present study may have relevance to the understanding of the formation of electrostatic shocks and solitons in laboratory produced pair-ion plasmas.

Instability of higher harmonic electrostatic ion cyclotron waves in a negative ion plasma

AbstractWe present a kinetic theory analysis of the electrostatic ion cyclotron (EIC) instability in a plasma containing positive ions, electrons, and negative ions that are much more massive than the positive ions. Conditions are investigated for exciting the fundamental and the higher harmonic EIC waves associated with each ion species. We find that as the concentration of heavy negative ions increases, the wave frequencies increase, the unstable spectrum in general shifts to longer perpendicular wavelengths, and the growth of higher harmonic EIC waves tends to increase within certain parameter ranges. Applications to possible laboratory plasmas are discussed.

Probe Measurements in Electronegative Plasmas: Modeling the Perturbative Effects of the Probe‐Holder

AbstractA basic property of an electronegative plasma is its separation into two distinct regions: an ion‐ion region far from boundaries, where the densities of positive and negative ions are higher then electron density, and a near‐boundary electron‐ion region, where negative ions have practically negligible density. This is due to the influence of the ambipolar electric field, which depends on electron (not negative ion) plasma parameters. This electric field “holds off” negative ions from the boundary, as the ions have lower mobility and temperature compared to the electrons. Therefore, negative ions will be repelled by any object inserted into the plasma. This can lead to errors in measurements of negative ion and electron parameters by any invasive method. Numerical modeling of electric probes in an argon‐oxygen plasma clearly demonstrates possible errors of direct measurements of negative ion probe current. This can also affect results from the photo‐detachment method and direct measurements of negative ion energy distribution (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)